The goal of this proposal is to develop and evaluate an innovative MRI compatible robot for improved bone biopsy in pediatrics. The robot will enable a new paradigm for rapidly evaluating suspicious bone lesions through image-guided biopsy. This will enable a novel clinical workflow defined with the goal of minimizing trauma and radiation exposure. The robot would have important applications in diagnosing and distinguishing bone cancers and bone infections, greatly facilitating clinical decision-making and therapy management. Malignant bone cancers are the third most common pediatric solid tumors after lymphoma and brain cancers and include osteosarcoma and Ewing sarcoma, with thousands of cases in the US alone. Accurate histologic diagnosis is critical for the planning and initiation of surgery, chemotherapy, and or radiation therapy. Osteomyelitis is a bone infection, with over 50% of reported cases seen in pre-school age children. Accurate diagnosis of the presence of bone infection and the infecting organism is critical for optimal therapy. Importantly, the imaging appearance of neoplastic and infectious pathology can be indistinguishable, making targeted and rapid tissue sampling key to clinical management. Our specific aims are to: 1. Design, construct, and evaluate a pneumatic, MRI compatible robotic-assistant system for long bone biopsy in pediatric patients. The robot will be placed along the limb of the child in the MRI scanner and will precisely orient a needle-guide for biopsy based on the images. The physician will perform the biopsy manually through the needle-guide. 2. Develop a path planning workstation for image-to-robot registration, selecting the location of the target, navigation and targeting based on the images, and means of trajectory verification before manual needle insertion for biopsy. 3. Integrate the robot with the planning workstation and evaluate the system in the MRI environment using custom anthropomorphic pediatric phantoms and goat legs. Modify the system as needed and repeat the evaluations to validate the system in-vitro. 4. Conduct a pilot safety and feasibility clinical trial on ten subjects.